In the course of activities by humans in order to maintain life, itches felt in the skin on the surface of a human body are a sensation, itching, caused by weak stimulation to the pain spot on the skin or the mucous membranes.
In recent years, incidences of atopic dermatitis have dramatically increased with changes in living environment. It is thought that environmental factors contribute greatly to the onset of atopic dermatitis. The environmental factors are divided into the non-allergic factors and the allergic factors. The non-allergic factors include, dry skin, sweating, pressure or weight load onto the skin, scratches on the skin and the like. The allergic factors include those caused by the aspiration of food allergens, contact to mites, house pets, pollens, metals and the like.
In the case of non-allergic factors, contact with a factor causes an itchy sensation, in response to which one scratches the skin resulting in the destruction of skin tissues, the breakdown of protective functions of the skin, and the onset of cutaneous hypersensitivity and infectious conditions caused by pathogens.
Allergic conditions caused by the production of immunoglobulin E (IgE) derived from antigen-antibody reaction occurring in vivo, which then stimulates the cell membrane of mast cells to release active substances such as histamine, leucotriene, serotonin and the like. Thanks to their ability of promoting vascular permeability and constricting smooth muscles, these substances thus liberated cause the leakage of leukocytes or proteins from the blood vessel and bronchoconstriction by inflammation which may cause asthma. The entry of allergen into the body sensitizes T cells, which, when contacted to the same allergen again, release inflammatory factors called lymphokines which cause reactions. Against such conditions, studies are being performed in order to search agents effective for the prevention and improvement thereof.
In this connection, there have been known those that make use of the ability of borneol to stabilize the membrane of mast cells (Japanese Unexamined Patent Publication (Kokai) No. 6-211713), those that make use of inflammation-inhibiting effect by the culture liquid of streptomyces (Japanese Unexamined Patent Publication (Kokai) No. 5-25053), and the like. Also, it is known that the intake of sesame oil can inhibit the production of leucotrienes that are responsible for allergic reactions (Prostaglandin, Vol. 36, No. 3, 1988). There are also known one that makes use of the anti-allergic property of lipids containing docosahexaenoic acid (DHA) or linolenic acid (Japanese Unexamined Patent Publication (Kokai) No. 2-29081). Indeed these naturally occurring anti-allergic agents have few adverse reactions, but their effect is not sufficient for the prevention and treatment of anti-allergic conditions.
Since the release of a variety of active substances represented by histamine from mast cells and basophils is responsible for the above anti-allergic conditions, inhibitors of histamine receptors are considered to be effective for alleviating the conditions, and anti-histamines such as chlorphenylamine and diphenhydrakine and adrenocortical hormones have been used. But there is a problem that the use of these agents is accompanied by adverse reactions.
From the foregoing, pharmaceutical agents with smaller adverse reactions are being developed, and substances derived from naturally products are being developed.
As such natural products, those that use the petal extracts of the genus Helianthus of the family Asteraceae (Japanese Unexamined Patent Publication (Kokai) No. 2000-351723), extracts of Cinchona succirubra (Japanese Unexamined Patent Publication (Kokai) No. 2000-26307), extracts of Melaleuca Alternifolia (Japanese Unexamined Patent Publication (Kokai) No. 11-255661), tocopherol extracts (Japanese Unexamined Patent Publication (Kokai) No. 2001-163764), those that use chitosan (Japanese Unexamined Patent Publication (Kokai) No. 2001-55335) etc. are being developed.